The present invention generally relates to electronic data communication systems. In particular, the invention relates to a technique for managing multiple electronic data subscribers in an efficient manner at a central site.
The advent of Internet service and video communication, among other advances associated with the transmission of electronic data, has generated an increased consumer desire for electronic data transfer to and from an equipment terminal such as a computer, television, or the like. This increased desire has generated an increased demand for communication providers, such as telephone companies and Internet service providers, to handle increasing amounts of data.
Existing telephone infrastructures such as the public switched telephone network (PSTN) may be used to transfer both telephone service (e.g., voice band data) and electronic data (e.g., video with or without accompanying audio) to and from a telephone or terminal. Using an existing telephone network infrastructure to transfer data to and from a terminal allows communication providers such as telephone companies to leverage their existing telephone connections to households for both voice and data transfer. In particular, existing phone lines of the PSTN, typically twisted-pair wires, may be used to transmit both telephone service and data. The twisted-pair wires may generally transmit data at frequencies up to several MHz; however, the PSTN generally includes filters and data sampling apparatus that limit voice frequency bandwidth to about 3000 Hz. Consequently, data transfer over the PSTN is also generally limited to a bandwidth of about 3000 Hz, absent modifications to the PSTN.
Digital subscriber line (DSL) communication systems and the like may be used to transmit information over twisted-pair wires over a greater bandwidth, e.g., up to several MHz by bypassing the voice frequency digital sampling apparatus and at least some of the PSTN filters. DSL systems generally include a subscriber modem attached to a subscriber terminal and a corresponding system modem located within or proximate a central office of the PSTN. The system modem typically includes analog-to-digital converters, digital-to-analog converters, and bit pumps to convert electronic information into appropriate formats for transmission over PSTN lines.
Because space requirements and power consumption at the central office increases with each additional modem in the central office, it may be desirable to minimize the number of modems or processors in the central office. Also, data transmitted over communication lines typically occurs in bursts; i.e., there may not be a continuous stream of data. Hence, the central office may be able to provide data transfer service to a number of subscribers that exceeds the actual number of modems or processors resident at the central office. In other words, it may provide oversubscription of data transfer services.
A DSL system that allows oversubscription of consumer modems to a central office is disclosed in U.S. Pat. No. 5,668,857, issued Sep. 16, 1997 to McHale. The system disclosed in the McHale patent includes a communication server, located within a central office of a PSTN, which includes a switch, a modem pool, and a controller connected to both the switch and the modem pool. The controller detects a need for data transfer service from the subscriber and directs the switch to couple the subscriber transfer line to a selected subset of modems in the modem pool. The switch disclosed in the McHale patent is analog, i.e., the format of the signal is analog on both the input and output data lines connected to the switch. An output signal from the switch is transferred to the system modem, which converts the signal from an analog format to a digital format.
Analog switching of data lines connected to modems may be inadequate in several regards. For example, analog switching may be inefficient because, in part, when data is transmitted to a subscriber modem, time is required to determine which system modem will connect to the subscriber modem, and time is required to form the connection. Analog switching techniques may require additional system modems located within or near the central office to overcome the time requirements for modem selection and switching.
Additional problems with using analog switching of lines that are transmitting data in analog format may include the generation of transients in a circuit as the switch is activated and deactivated. Additionally, analog switching may be unreliable and require significant board space at the central office. For these reasons and others, analog switching of data communication lines may be relatively expensive. Therefore, improved methods and apparatus for efficiently handling multiple data transmission subscribers are desirable.
The present invention provides an improved method and apparatus for transmitting voice and electronic data over a public switched telephone network. While the way in which the present invention addresses the drawbacks of the now-known data communication systems and components thereof will be described in greater detail hereinbelow, in general, in accordance with various aspects of the present invention, the inventive apparatus provides an improved communication system that allows a fewer number of system data pumps (which modulate and demodulate information) than a number of subscribers desiring data communication. In addition, the inventive system is configured such that the system does not require analog switching to connect subscribers to the data pumps. Thus, unwanted problems such as time delay associated with analog switching methods and apparatus are reduced.
In accordance with an exemplary embodiment of the present invention, the communication system includes a number of data converters, each configured to connect to a subscriber modem or terminal, and a number of data pumps, wherein the number of the data converters is greater than the number of data pumps.
In accordance with another embodiment of the present invention, each converter includes an analog front end configured to communicate with the subscriber modem or terminal, an analog-to-digital converter, and a digital-to-analog converter.
In accordance with a further embodiment of the present invention, a plurality of converters are connected to a single data pump. Multiple converters may also be connected to multiple data pumps.
In accordance with another embodiment of the present invention, the data pump broadcasts data simultaneously to all subscriber modems or terminals attached to the data pump. The data includes information to identify the subscriber modem or terminal which is to convert and decode the data for a particular subscriber""s use.